Heavy duty tractor-trailer transmissions, often referred to as Class 8 transmissions, are adapted to be manually shifted to provide several different speed ratios. A plurality of gears are supported along a shift shaft, which can be moved or shifted along a shift axis to change to a desired gear ratio from amongst one of the plurality of gears. Typically, multiple shift shafts are used to provide a greater range of gear ratios. Controls are required to provide smooth shifts during range shifting between the different shift shafts.
Class 8transmissions have increased in complexity as traditional pneumatic controls have been converted to electric controls. In a typical pneumatically controlled system, the shift shafts were each mechanically linked to a slave valve in order to control when range shifts occur. This was accomplished by using a checkshaft that moved perpendicularly relative to the shift axis in response to axial movement of any one of the shift shafts.
When pneumatically controlled systems were replaced by electric controlled systems, the slave valve was replaced by a neutral switch and pin assembly. The pin actuated the neutral switch in response to movement of the checkshaft. In both types of controls, the goal is to ensure the main transmission is in neutral (i.e., no gear is engaged in the main transmission) when the range shift occurs. One disadvantage with this configuration is that movement of the checkshaft in such a manner adversely affects drive shift feel.
Thus, there is a need for a neutral switch system for a vehicle transmission that does not require a checkshaft.